The present invention relates to a dual tone multi frequency address signal (DTFM) sender system or a push-button (PB) sender system for a push-button type key telephone system or a simplified telephone exchange system, and particularly relates to a PB sender system having a common DTMF oscillator.
A prior push-button type simplified telephone exchange system has many wires between each telephone set and a common unit. Each telephone set must include an individual DTMF oscillator. Therefore, the structure of the telephone set is complicated and the cost of the system is expensive. Further, the larger the system, the more wires between each telephone set and the common unit is needed. Accordingly, in a prior simplified telephone exchange system, a system having more than thirty telephone sets is almost impossible.
A proposal for overcoming the above disadvantage is to provide a speech path contact in a common unit and reduce the wires between each telephone set and said common unit. However, in this system, each telephone set must still have individual DTMF oscillators. Therefore, many DTMF oscillators are necessary.